This invention relates to a method and apparatus for sensing angular displacement and can be used, for example, for measuring directional changes of a moving object.
Conventional apparatus exist for sensing the angular displacement, or turn of an object. These apparatus may detect changes in angular displacements of an object and provide outputs that may be used to determine such indications as location, heading, rotational speed, among others. These indications may be particularly useful when the object is a vehicle and where the operator needs to know the location and/or heading of the vehicle. A gyroscope is one such conventional apparatus used for sensing turn of an object.
A gyroscope typically includes a rotating object mounted within an enclosure, wherein the object rotates in a reference axis at a high rate of speed. The object is generally mounted on a complicated set of bearings so that when the enclosure moves, no net torque acts to change the objects"" direction of angular momentum. However, these changes in angular momentum are sensed by the gyroscope. The rotating object generally must rotate at high speeds for certain mathematical assumptions to accurately describe the object""s motion. When the gyroscope is mounted to an object, the gyroscope detects changes of angular momentum which may be used to determine changes in angular displacement. Angular momentum is proportional to angular velocity, and thus angular displacement may be determined from angular velocity generally through an integration calculation.
As discussed above, a gyroscopic apparatus may be used to detect changes in the angular rate of movement of an object. A typical gyroscopic apparatus used for this purpose generally includes a disk that rotates at high speed, e.g. from a few thousand rpm to upwards of 20,000 rpm. The disk may be flexible or include flexible members that extend from an axis of rotation of the gyroscope. As the disk is rotated, any movement about an axis perpendicular to the axis of rotation of the disk will cause the flexible disk members to flex toward and away from a plurality of plate members, changing a capacitance between the plate members and the flexible disc members. An electrical circuit is provided to generate a signal based on the changing capacitance. This signal is used to determine the movement of the object about a reference axis. The signals are generally interpreted by a system which provides indications or performs corrective actions relating to the angular movement of the object. For example, one such system may provide a heading indication onboard a vehicle, the heading indication being used for navigational purposes. One such angular rate gyroscope is disclosed in U.S. Pat. No. 4,811,613 issued Mar. 14, 1989 to Phillips et al.
Drawbacks of conventional gyroscopic sensors include a susceptibility to frequent failures of the moving parts, particularly the motor that rotates the disk at high speed. The mean time between failures (MTBF) of conventional gyroscopic sensors is directly related to the number of rotations of the motor. Because frequent failures occur, the gyroscopic sensors must be frequently serviced and calibrated. Conventional sensors are also sensitive to vibration and gravity. Further, these sensors generate electrical noise because of the frequency of motor rotation.
One embodiment of the invention is generally directed to a method for sensing and measuring angular displacement of a rotating object. A method is provided for measuring angular motion of the rotating object be providing a reference object for the rotating object such that the reference object maintains an independent angular position despite a rotational motion of the object. Further, the method includes measuring the rotational motion of the object by measuring an angular displacement of the object with respect to the angular position of the reference object.
In another aspect, an apparatus is provided for measuring a displacement angle of a rotating object. The apparatus includes a container having a fluid, a reference object that is allowed to rotate freely within the container and is positioned within the container, and a sensing element configured to sense an angular displacement of the rotating object with respect to the reference element.
In another aspect, an apparatus is provided for measuring a displacement angle of an object. The apparatus includes a reference coupled to the object so that the reference object independently maintains an angular position despite the rotational motion of the object and a reference device that is coupled to the object. The reference device includes an angular compensator having an output providing a control signal that controls rotation of the reference device with respect to the object so that the reference device maintains an angular relationship with the reference object and a position unit having an input that receives the control signal and an output that provides an indication of the rotational motion of the object based upon the control signal.
In another aspect, a method is provided for measuring a displacement angle of an object. The method includes steps of arranging a reference object so that the reference object is coupled to the object but does not move in the direction in response to the angular motion of the object, controlling a reference device to move in relation to the reference object so that the reference device substantially maintains an angular relationship with the reference object and measuring the angular motion of the object based upon an amount that the reference device is controlled in the step of controlling.
Advantageously, various"" embodiments do not require a motor that rotates at high frequencies because the sensor detects angular displacement directly in contrast to conventional gyroscopes that sense changes in angular momentum by precession. Further, various embodiments are less susceptible to vibrations or lateral accelerations than conventional sensors due to the damping effect of a liquid within the sensor. Also, because various embodiments include a motor that rotates at lower frequencies than those of conventional sensor devices, less radio frequency interference (RFI) noise is generated by the sensor. In addition, because there are fewer moving parts and the frequency of motor rotation is less than that of conventional sensors, motor life expectancy is greater for one embodiment than that of conventional devices. These and other advantages are provided by the following embodiments and methods.
Further features and advantages of the present invention as well as the structure and operation of various embodiments of the present invention are described in detail below with reference to the accompanying drawings. In the drawings, like reference numerals indicate identical or functionally similar elements. Additionally, the left-most one or two digits of a referenced numeral identifies the drawing in which the reference numeral first appears.